CodeGen: TII: Take MachineInstr& in predicate API, NFC

Change TargetInstrInfo API to take `MachineInstr&` instead of
`MachineInstr*` in the functions related to predicated instructions
(I'll try to come back later and get some of the rest).  All of these
functions require non-null parameters already, so references are more
clear.  As a bonus, this happens to factor away a host of implicit
iterator => pointer conversions.

No functionality change intended.

llvm-svn: 261605
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 5cc7ba6..6421b8c 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -691,7 +691,7 @@
     // is possible. The isPredicated check is needed because this code can be
     // called during IfConversion, where an instruction which is normally a
     // Barrier is predicated and thus no longer an actual control barrier.
-    return empty() || !back().isBarrier() || TII->isPredicated(&back());
+    return empty() || !back().isBarrier() || TII->isPredicated(back());
   }
 
   // If there is no branch, control always falls through.